1. Field of the Invention
The present invention relates to a method for producing a winding for electrical machines wherein a number of conductor elements are fitted on a winding former, a winding for an electrical machine having a large number of conductor elements which are carried by a winding former and form a number of turns, and an electrical machine.
2. Description of the Related Art
Electrical machines, such as synchronous machines, have slots in which one or more current-carrying windings are placed. The slots with the windings can be located, for example, in the stator or else in the rotor of the electrical machine. During operation of such electrical machines, however, a non-uniform current distribution can in certain circumstances occur across the copper or conductor cross section in the slots. The slot height as well as the frequency of the current are significant factors in this case.
The non-uniform current distribution or one-sided or two-sided current displacement occurs in particular in large machines with bar windings and in the rotor bars of asynchronous squirrel-cage rotors. However, current displacement can also occur in the stators of small machines, for example if they are operated at high frequencies in order to achieve better utilization. These frequencies may be more than two kilohertz, with the operation of such electrical machines being made possible by modern converter technology.
In asynchronous motors, the effect of the non-uniform current distribution is advantageously used to increase the rotor resistance during starting, when a high slip frequency occurs.
Owing to the increase in the resistive heat losses, the current displacement is undesirable. Attempts have therefore been made to suppress the current displacement in windings through which alternating current or a current which changes with time flows during operation.
Various measures for suppressing current displacement are known, such as subdividing the conductor into parallel conductor elements, thus resulting in smaller conducting heights for the same conductor width. In this case, conductors located one above the other may have different conductor heights. Owing to the stray flux linking between the conductor elements, subdivision into parallel conductor elements generally does not lead to adequate suppression of current displacement.
In order to suppress the current displacement more effectively, attempts have therefore been made to form the conductor elements into layers. In the process, the sequence of the conductor elements in the slots is changed. In the case of two-layer windings, this results naturally as a consequence of the end winding design. Owing to the change in the sequence of the conducting elements in the slots, the integration path which governs an eddy current path has comprises field elements in opposite directions. This means that the individual flux elements partially compensate for one another, and the resultant flux linking becomes less.
Synthetic bars result in the stray flux linking within the slot area of an electrical machine formed from any two conductor elements disappearing completely. Such synthetic bars are subdivided conductors whose layers within the slot region are configured such that the flux linking of every possible eddy current path passing through the conductor elements disappears.
One known synthetic bar is the transposed conductor which is illustrated in FIGS. 2a and 2b. In this bar, the conductor elements uniformly pass through all the height layers in a slot and leave the slot in the same height layer in which they enter the slot.
DE 197 54 943 A1 describes a double transposed conductor for the winding of an electrical machine, in which conductor elements are arranged in a number of adjacent stacks. Two adjacent conductor elements are in each case routed as a conductor element pair alongside one another over the entire length of a conductor, and are twisted as they do so. To achieve the desired twisting, the conductor elements are not only bent parallel but are also bent to be crossed over, in order to achieve optimum compensation for the transverse and radial fields during operation of the electrical machine.
The known synthetic bars including transposed conductors have the disadvantage, however, that they cannot be produced using modern automatic winding machines. Furthermore, the frequent crossing over of the conductor elements in the slot area, with the conductors being routed obliquely, leads to greater conductor element lengths and to poorer copper filling factors in the slot.
The object of the present invention is thus to specify a method for producing a winding for electrical machines which can be carried out more easily and by means of which a winding with an improved filling factor and adequate suppression of current displacement can be achieved. Furthermore, it is intended to provide a winding for an electrical machine, and an electrical machine, in which, during operation, current displacement is adequately suppressed, and which winding can also be produced by machine with a high filling factor.
This object is achieved by the method for producing a winding for electrical machines wherein the conductor elements (L1, L2, L3) are aligned parallel to one another in a predetermined order while being wound onto the winding former and, while being wound, the predetermined order is reversed in at least one place on the winding former. Advantageous features, aspects and details of the invention are evident from the description and the drawings. Advantages and features which are described with reference to the method likewise apply to the apparatus, and advantages and features which are described with respect to the apparatus likewise apply to the method according to the invention. Analogous statements apply to the electrical machine.
In the method according to the present invention for producing a winding for electrical machines, a number of conductor elements are fitted on a winding former, with the conductor elements being aligned parallel to one another while being fitted onto the winding former, and with the parallel-aligned conductor elements being reversed at least once, for example jointly, while being fitted, so that, at least in places, they change their position on the winding former. It is thus possible to produce a winding with a high filling factor, in which case, furthermore, the winding can also be produced by machine, and by means of which current displacement is effectively suppressed during operation of the electrical machine.
The conductor elements are advantageously placed in a slot, with the conductor element which is located deepest in the slot being located furthest upward after reversal. It is thus possible to produce windings in the slots of electrical machines, in which windings the current displacement during operation is particularly low.
The conductor elements are preferably fed by means of guide elements, in particular by means of wire guide nozzles. The guide elements or wire guide nozzles are rotated through 180xc2x0, for example in order to reverse the conductor elements during the winding process. A number of parallel wires are thus fitted, for example, onto a rotating winding former, thus producing a winding with a specific number of turns, and at a defined feed rate.
The parallel alignment and the wires or conductor elements placed parallel alongside one another result in a particularly high copper filling factor which may be, for example, up to 20% greater than in the case of conventional winding production. The reversal of the conductor elements, or the rotation of the wire guide nozzles through 180xc2x0, results in the conductor elements being reversed in layers. This results in uniform stray flux linking of the conductor elements, and thus also uniform current distribution between the conductor elements, the number of which is governed, for example, by the number of wire guide nozzles.
The reversal of the conductor elements is preferably in each case defined by a number of turns wrev=w/(2+k), where w is the total number of turns to be fitted, and k may be equal to 0, 2, 4, 6 . . . etc. The constant k is a multiple of two, including the value zero. This results in reversal or layering in each case after an exactly defined number of turns, with that wire which was first of all located deepest in the slot now being located furthest upward after reversal.
k is preferably chosen to be as small as possible, which results in particularly well organized wire routing which at the same time guarantees a high filling factor.
Triple reversal, in each case after w/4, 2*w/4 and 3*w/4 turns, is particularly preferred during production of the winding, with w being the total number of turns to be fitted. This results in a sufficiently high statistical confidence level that the stray flux linking will be uniform. In this case, the copper filling factor still corresponds approximately to the value without reversal, and the uniform distribution of the overall current between the conductor elements is ensured with a sufficiently high statistical confidence level. On the other hand, the number of reversals is still sufficiently low to avoid irregularities during the winding process.
With a small constant k which is, for example, preferably zero or, in particular, preferably two, excessively frequent crossing of the wires in one layer is avoided, which would mean the wires in the next layer being spread apart from one another to a lesser or greater extent.
The reversal points are advantageously shifted as a function of the slot geometry, the total number of turns to be fitted and/or the winding scheme. Even better results can thus be achieved, depending on the application, such as particularly high filling factors and particularly uniform current distribution in the slot.
The number of turns which a conductor element which is furthest upward in a slot passes through is advantageously the same, or at least approximately the same, as the number of turns which the conductor element which is furthest downward passes through. This results in particularly uniform stray flux linking of all the conductor elements.
The winding former is, for example, a stator tooth of an electrical machine or else, in general form, an armature winding of an electrical machine or of an alternating current machine. The winding former may, however, also be in the form of a separate component, onto which the winding is first of all wound, and which is then fitted on to a stator tooth.
The method is preferably carried out by machine or using a winding machine. For example, the winding former is rotated under a number of wire guide nozzles in order to fit the parallel conductor elements, in order in this way to produce a winding with a large number of turns, and with a defined feed rate. This results in particularly cost-effective production which, furthermore, can easily be matched to the respective requirements.
The winding according to the invention for an electrical machine has a large number of conductor elements which are carried by a winding former and form a number of turns, with the conductor elements in the turns being arranged parallel alongside one another, and with the parallel conductor elements being reversed at least once and, in consequence, their positions being interchanged, at least in places.
This results in a particularly high copper filling factor in the slot of the electrical machine. The conductor elements are crossed over less frequently and run obliquely only at the reversal points. This results in shorter conductor element lengths, which likewise contributes to an improved filling factor. The current displacement is effectively suppressed, and the relatively simple routing of the conductor elements or wires even allows production using modern automatic winding machines.
The conductor elements which are located parallel alongside one another are preferably rotated through 180xc2x0 after each w/(2+k) turns, where w is the total number of turns and k may be equal to 0, 2, 4, 6, . . . etc. It is particularly preferable for the parallel conductor elements to be reversed three times, with a reversal point or reversal region occurring after w/4, 2*w/4 and 3*w/4 turns, and with w being the total number of turns. In this case, the winding has a copper filling factor which is approximately as great as that in a winding without reversals, but while nevertheless ensuring uniform distribution of the overall current between the conductor elements during operation of the electrical machine with a sufficiently high statistical confidence factor.
The reversal points are advantageously shifted with respect to one another on the winding former. This achieves an optimum result, depending on the slot geometry, the total number of turns and the winding scheme.
By way of example, the conductor elements are placed parallel alongside one another in a slot, with that conductor element which is located deepest in the slot before a reversal point being located furthest upward in the slot after the reversal point. The conductor elements are, for example, wires, in particular copper wires, and the winding former is preferably a stator tooth of an electrical machine or a separate winding former which is fitted on to a stator tooth after it has been wound.
According to a further aspect of the invention, an electrical machine is provided which has a winding according to the invention. The electrical machine may be, for example, a three-phase or alternating current machine, with the windings according to the invention being placed in the stator and/or rotor by means of slots.
The electrical machine can be produced cost-effectively, since the winding production can be carried out by machine. This machine has particularly low resistive heat losses, since the current displacement in the slots is effectively suppressed. Nevertheless, there is no need for complex wire or conductor routings, for example synthetic bars or transposed conductors.
One preferred embodiment of the invention will be described by way of example in the following text with reference to the figures.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.